Making sense out of 3 weeks Germany,Switzerland, and Austria

Oberdiessbach, Lake Thun, Lauterbrunnen, Grindelwald, and Wengen are all in the same area and can easily be visited by train from a central location such as Lauterbrunnen or Interlaken.

If you rent a car in Germany you can return it in another country, albeit there is probably a fee involved. Still, the fee may be worth it if it is convenient.

You could fly into Munich, rent a car, and then drive to Mittenwald. Then drive to Lake Constance, the BF area, then into Switzerland's Berner Oberland region. You could drop the car off in Interlaken once your done there and then take a train to Zurich or Geneva to fly home.

Fly in to Zurich, and by train to ...
1 Lauterbrunnen, Grindelwald and Wengen
2 Lake Thun and Oberdiessbach
Pick up a hire car in Freiburg, Germany
3 Black Forest
4 Lake Constance
5 Mittenwald and Garmisch-Partenkirken
Return hire car in Munich, and by train to ...
6 Salzburg and Hallstatt
Fly out of Munich or Vienna

i guess i didnt realize just how close Oberdeissbach was to Thun. This makes things easier. I think I will stay in Thun and visit each place in that area on daytrips. It will be alot easier on this old lady!! One hotel, no packing and unpacking. More time for sitting, eating, drinking, people watching..

Does anyone have any info on Oberdeissbach such as where is old cemetery? I have many relatives buried there. Last one was in 1850's that I know of before they came to America .. is it unreasonable to think I could find any graves this old?

i think having the rental car in Germany only is best idea.

Please suggest which of Lauterbrunnen, Grindelwald, & Wengen could be seen together in one day or should i do them separately. I will be doing no hiking.

How does this look?
DAY 1 ARRIVE ON TRAIN TO LAKE THUN
DAY 2 LAKE THUN
DAY 3 DAYTRIP TO OBERDEISSBACH ON TRAIN
DAY 4 LAKE THUN
DAY 5 DAYTRIP TO LAUTERBRUNNEN AND GRINDELWALD ON TRAIN
DAY 6 DAYTRIP TO WENGEN AND MURREN ON TRAIN
DAY 7 TRAIN TO FREIBURG GERMANY. GET RENTAL CAR
DAY 8 BLACK FOREST
DAY 9 BLACK FOREST
DAY 10 TO LAKE CONSTANCE
DAY 11 LAKE CONSTANCE
DAY 12 TO MITTENWALD and GARMISCH-PARTENKIRKEN AREA
DAY 13 MITTENWALD and GARMISCH-PARTENKIRKEN
DAY 14 MITTENWALD and GARMISCH-PARTENKIRKEN
DAY 15 MITTENWALD and GARMISCH-PARTENKIRKEN
DAY 16 MITTENWALD and GARMISCH-PARTENKIRKEN
DAY 17 RETURN RENTAL CAR THEN TRAIN TO SALZBURG,AUSTRIA
DAY 18 SALZBURG
DAY 19 DAYTRIP ON TRAIN TO HALLSTATT
DAY 20 SALZBURG
DAY 21 TRAIN TO VENICE

i could take one day away from MITTENWALD and GARMISCH-PARTENKIRKEN and add it to Berner Oberland area.

From Interlaken you go up the Lauterbrunnen Valley - Wengen and Grindelwald sit above the valley on one side, and Murren the other.

I'd lean towards staying a few nights on Lake Thun, and a few nights separately in Lauterbrunnen. Otherwise Interlaken for a compromise.

I would keep the car and base in the Salzkammergut (maybe St. Gilgen) for Salzburg and Hallstatt. I'd also take a "Mittenwald/Garmisch" night and add it here. Add a visit Berchtesgaden, Konigssee, Hohenwerfen Fortress, etc. while in the area.

Return the car just over the border from Salzburg in Freilassing, Germany.

I'd also see if you could base in Wengen or Lauterbrunnen and day trip from this base. I couldn't imagine staying in Thun and just visiting the Lauterbrunnen valley.

Lauterbrunnen may be better base as suggested. I am leaning toward keeping car for duration of trip now for several reasons. There are just too many towns I want to visit !! This will be better on my own schedule, mobility and ability to change my mind on a given day throughout my vacation.